A cell autonomous molecular clock temporally organizes many essential physiological functions. Disruption of the clock thus has numerous consequences for health. Forward genetic screens have identified multiple clock components and the core principles of the clock are highly conserved. Recently, our collaborator discovered a golden hamster (Mesocricetus auratus) with a spontaneous mutation (Theta) that results in a dramatic elongation of the hamster's endogenous period. The focus of this proposal will be to elucidate how this mutation disrupts known relationships between core clock genes and, eventually, to identify the mutation in the hamster genome. I will look at mRNA and protein expression dynamics in tissue to identify alterations in the relationships between known clock genes. To determine whether period elongation is a cell autonomous feature of the Theta clock, I will use cell-based real time luminescence reporters in primary fibroblast cultures. Finally, using whole genome sequencing and bulk segregation analysis, I will identify a candidate region in the hamster genome and narrow the field of variants through cellular assays until the causative mutation has been determined. Ultimately, Theta will provide insight into the mechanisms governing the correct timing of the endogenous clock.